One advantage of displays of the color sequential type is the possibility to produce color display systems for direct-view screens without colored filters, that is to say without color information attached to a picture dot (pixel). Each picture dot is colorless and a lightbox is used which makes it possible successively to illuminate the display in the three primary colors, typically, in red, in green and in blue.
Addressing then comprises several color frames for each complete video frame. In the time of each color frame, all the pixels of the matrix are addressed to display the video information corresponding to the associated primary color, and the lightbox illuminates the display in the corresponding primary color.
A corresponding color sequence is illustrated in FIG. 1: In each frame, F1 for example, three color frames, red, green and blue, in the example fR1, fG1 and fB1 respectively, follow one another. The red, green, blue color sequence is repeated periodically at the frequency of the complete video frames. In the example, the frame frequency is equal to 60 Hz giving a duration T0 of 16.667 ms for each video frame.
A known problem with these displays is the problem called “color break-up”, due to the stabilization time of the liquid crystal, which results in a display defect that is perceptible to an observer's eye. Specifically, because of the ability of the eye to distinguish very rapid movements, it is capable of distinguishing the succession of the various color frames. Notably, an observer perceives color flickering that is particularly visible on a white picture when the screen operates at low frequency or when he moves his head in front of the screen. Although the eye accepts without too much trouble a complete refresh of the pictures at 50 Hz, a change in the colors at the frequency of 150 Hz can be detected in the observation situations as cited above.
The eye's perception of this display defect takes the form of a succession of colored bands or fringes, typically the succession of the primary colors, as illustrated schematically in FIG. 1, with a spatial frequency which depends on the refresh frequency of the picture. Therefore, in the example, the eye perceives a periodic succession of a red band, a green band and a blue band.
It will be noted here that, by convention, the red is depicted in white dots on a black background, the green in oblique black dashed lines on a white background and the blue by a grid of black lines on a white background.
To solve this display defect problem due to the periodic succession of the color frames, an effort is usually made to increase the frequency of the video frames, in particular to double it. The color break-up effect is lessened. Nevertheless it still remains clearly visible, because it is not possible to refresh the picture at too high a frequency for reasons of technological compatibility with active matrix screens. Also the picture frequency remains well below the threshold defining the limit of perception of the phenomenon, according to the visual acuity of a standard observer.